Multi-loop natural circulation coupling heat extraction experiment system

Abstract

The invention discloses a multi-loop natural circulation coupling heat removal experiment system, which relates to the technical field of nuclear reactor safety, and is characterized by comprising an integrated pressure vessel, an energy conversion and residual heat removal integrated design loop, a condenser cooling water loop, a thermal insulation material and a measuring instrument, the heat insulation material coats the heat extraction experiment system and is used for reducing energy leakage; and the measuring instrument is arranged on the heat extraction experiment system and is used for measuring and monitoring the flow, the temperature, the pressure and the liquid level. Research is carried out on an integrated pressure container designed in a marine nuclear power source and an energy conversion and waste heat removal integrated system, and three natural circulations are formed in a secondary loop and a condenser seawater section in the integrated pressure container respectively; all natural circulations are coupled into a whole through a steam generator heat transfer pipe and a condenser heat transfer pipe, and waste heat of a reactor core is discharged through coupling of multiple natural circulations, so that shutdown safety of a nuclear reactor is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear reactor safety, and more specifically to a multi-loop natural circulation coupled heat removal experimental system. Background Art

[0002] Nuclear power is a way to generate electricity through a self-sustaining chain fission reaction using fissile nuclides. At present, nuclear power is widely used in land-based nuclear reactors to provide power for land-based power grids. my country has rich marine resources, including undeveloped islands in vast sea areas, offshore drilling platforms, seabed exploration and deep-sea detection workstations, etc., which require a stable and reliable power supply. Due to the complex deep-sea environment and extremely high requirements for equipment, traditional power supply methods are often difficult to meet the needs. Small nuclear power sources in marine environments have become an important energy choice in the process of marine resource development due to their high energy density, long life, and stable and reliable characteristics. They have broad application prospects in the field of marine resource development.

[0003] The existing designs of marine nuclear power systems mostly follow or draw on the original marine nuclear power technology. The system composition is relatively complex, construction and maintenance are difficult, and there is a great deal of uncertainty in both cost and cycle. Most small nuclear power designs adopt active and passive safety system design. The system is complex, which makes it difficult to arrange equipment and structures in offshore nuclear power systems. Among them, due to the different temperatures of different parts of the fluid and even phase changes, there is a density difference between different parts of the fluid. When the colder fluid is at a higher altitude than the hotter fluid, natural convection will occur under the influence of buoyancy. Its flow in the pipeline is also called natural circulation. The establishment and flow of natural circulation are affected by the floating driving force brought by the elevation difference between the cold and hot fluids, the resistance along the various parts of the flow channel, the local resistance brought by various equipment on the flow channel, such as valves, elbows, flow distribution plates, heat exchangers, etc., and the heat exchange between the fluid or working medium and the cold and heat sources in the circulation pipeline. The key parameter natural circulation flow rate fluctuates. The size of the driving force also determines whether the natural circulation flow can be fully established and run smoothly. There is also a great deal of uncertainty in the thermal conductivity of the entire loop.

[0004] Therefore, based on the above problems, the present invention aims to provide a multi-loop natural circulation coupled heat removal experimental system. By greatly simplifying the structural design of the marine nuclear power source and adopting an integrated design of energy conversion and waste heat removal, it is possible to form a multi-loop coupled natural circulation under accident conditions, extract the core waste heat, and achieve high inherent safety of the nuclear power source. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-loop natural circulation coupled heat removal experimental system. The present invention conducts research on the integrated pressure vessel and the integrated system of energy conversion and waste heat removal designed for marine nuclear power sources. It can form three natural circulations in the integrated pressure vessel, the secondary circuit and the condenser seawater section respectively. Each natural circulation is coupled into one through the steam generator heat transfer tube and the condenser heat transfer tube. The core waste heat is discharged by relying on the coupling of multiple natural circulations, which can be used to ensure the safety of nuclear reactor shutdown.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: a multi-loop natural circulation coupled heat removal experimental system, comprising an integrated pressure vessel, an energy conversion and waste heat removal integrated design circuit, a condenser cooling water circuit, a thermal insulation material and a measuring instrument; the thermal insulation material is coated on the heat removal experimental system to reduce energy leakage; the measuring instrument is arranged on the heat removal experimental system to measure and monitor the flow, temperature, pressure and liquid level;

[0007] The integrated pressure vessel includes a heat exchanger, a pressure stabilizer system and a temperature control and heating system; the heat exchanger is a plate heat exchanger, the pressure stabilizer system is arranged on a supporting platform above the side of the pressure vessel, and the temperature control and heating system is used to automatically cut off the power according to the highest temperature in the stack;

[0008] The energy conversion and waste heat discharge integrated design loop includes a steam turbine simulation body, a condenser, a deaerator simulation body, a feed water pump simulation body pipeline, a No. 1 water tank and a valve; the steam turbine simulation body is treated as a resistance component, the condenser adopts a shell and tube heat exchanger, the steam flows on the shell side, and the cooling water flows on the tube side. The condenser itself has a certain elevation difference to improve the natural circulation capacity of the cooling water on the tube side. The deaerator is simulated by a valve, the feed water pump simulation body pipeline is simulated by a valve, and the No. 1 water tank is used for loop filling and drainage;

[0009] The condenser cooling water circuit includes a condenser tube side and a No. 2 water tank; the condenser tube side adopts a U-tube layout, and multiple independent groups of pipelines are arranged in the condenser, which are synchronously connected to the cooling water tank No. 2 to ensure natural circulation capacity, as well as flow distribution and heat discharge balance of each loop; the No. 2 water tank is used to simulate the low temperature environment of ocean flow by slowly injecting and discharging equal flow rates of cold water.

[0010] The present invention is further configured as follows: the integrated pressure vessel is specifically designed to have an operating pressure of 1 MPa in the test heating section, a fluid temperature range of 135-180°C, and a single phase. The pressure vessel is made of 304 stainless steel, and a heating element through hole and a core simulation body are provided at the bottom to simulate the heat release of the core by electric heating.

[0011] The present invention is further configured such that a distance of at least 0.2 m is provided between the integrated pressure vessel and the support platform to facilitate drainage and arrangement of heating element wires.

[0012] The present invention is further configured as follows: a drainage channel is provided below the integrated pressure vessel for draining water from the vessel.

[0013] The present invention is further configured as follows: the operating environment of the integrated energy conversion and waste heat discharge design loop is specifically designed to have a design operating pressure of 0.2 MPa, a temperature range of 30-120°C, the fluid working medium is in a single-phase-two-phase fluctuation change state, and a phase change occurs between the steam generator and the condenser to avoid flow instability.

[0014] The present invention is further configured as follows: the operating environment of the condenser cooling water circuit is specifically designed to be a normal pressure condition with a temperature range of 20-80°C, the fluid working medium is in a single-phase state, boiling occurs, and natural circulation occurs on the condenser tube side. The heat source comes from the heat release of the condenser steam, and the cold source comes from the cold water in the water tank.

[0015] The present invention is further configured as follows: the measuring instruments are specifically flow meters, thermocouples, pressure gauges and liquid level gauges, which are used to measure and monitor the flow, temperature, pressure and liquid level of the heat removal experimental system.

[0016] The present invention also provides an experimental verification method for a multi-loop natural circulation coupled heat removal experimental system, comprising the following steps:

[0017] S1. Combine system simulation and refined numerical simulation of local flow and heat transfer phenomena in key equipment to optimize the size parameters and thermal hydraulic parameters of structures and equipment in the overall preliminary design of relevant systems;

[0018] S2. Using a bidirectional multi-stage modeling method, under non-isobaric and isophysical conditions, the overall circuit and key equipment are designed and analyzed for proportionality and flow resistance, and an experimental platform for a multi-circuit natural circulation coupled heat removal experimental system is built;

[0019] S3. Research on the operating characteristics and impact analysis of the multi-natural circulation coupled heat removal system is carried out for various accident conditions. The flow instability of the single-phase and two-phase coupled natural circulation with low head difference and high flow resistance is studied to obtain the transient response characteristics of the system and verify the operational feasibility and robustness of the multi-loop natural circulation coupled heat removal experimental system.

[0020] In summary, the present invention has the following beneficial effects:

[0021] 1. The present invention conducts research on the integrated pressure vessel and the integrated system of energy conversion and waste heat removal designed for marine nuclear power sources, and can form three natural cycles in the integrated pressure vessel, the secondary circuit and the condenser seawater section respectively. Each natural cycle is coupled into one through the steam generator heat transfer tube and the condenser heat transfer tube. The core waste heat is discharged by coupling multiple natural cycles, which can be used to ensure the safety of nuclear reactor shutdown;

[0022] 2. The present invention conducts system simulation, local area refined numerical simulation and multi-loop natural circulation coupled heat removal system experimental research, conducts research on the flow and heat transfer characteristics of low-level difference and high-flow resistance single-phase-two-phase coupled natural circulation system, verifies the feasibility and robustness of system operation, obtains the system transient response characteristics and stable operation boundary range, which are used to support the design of integrated marine nuclear power system and equipment structure optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a multi-loop natural circulation coupled heat removal experimental system in an embodiment of the present invention;

[0024] Figure 2 It is a simulation schematic diagram of the device prototype in the simulation experiment in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following is combined with Figure 1-2 The present invention is described in further detail.

[0026] Embodiment: A multi-loop natural circulation coupled heat removal experimental system includes an integrated pressure vessel (primary loop), an energy conversion and waste heat removal integrated design loop (secondary loop), a condenser cooling water loop (third loop), insulation materials and measuring instruments. The insulation materials are coated on the heat removal experimental system to reduce energy leakage. The measuring instruments are set on the heat removal experimental system to measure and monitor flow, temperature, pressure and liquid level.

[0027] The design of thermal hydraulic operation parameters in this embodiment is shown in Table 1:

[0028] Table 1 Thermal hydraulic operation parameter design table

[0029] parameter One circuit Secondary circuit Three circuits Design under pressure ~1.5MPa ~0.5MPa ~0.1MPa Operating pressure ~1.0MPa ~0.1MPa(normal pressure) ~0.1MPa Circuit temperature range 135℃～170℃ 135℃～170℃ 135℃～170℃ Heating power 1KWe~100KWe \ \ Water tank temperature \ 80℃ 23℃ Water tank volume \ <![CDATA[1m 3 ]]> <![CDATA[2m 3 ]]> Design Integrated pressure vessel Dual loop, equipment sharing Multiple independent pipelines

[0030] The integrated pressure vessel in the test heating section is specifically designed to have an operating pressure of 1 MPa, a fluid temperature range of 135-180°C, and is single-phase. The pressure vessel is made of 304 stainless steel, and has a heating element through hole and a core simulation body at the bottom, which are used to simulate the heat release of the core by electric heating. The integrated pressure vessel is set on a supporting platform, and a distance of at least 0.2m is set between the integrated pressure vessel and the supporting platform to facilitate drainage and arrangement of heating element wires. At the same time, a discharge channel is set under the integrated pressure vessel for container drainage.

[0031] In this embodiment, the integrated pressure vessel (primary circuit) specifically includes a heat exchanger, a pressurizer system and a temperature control and heating system; the heat exchanger adopts a plate heat exchanger, the pressurizer system has a pressurizer tank, a matching pressure-stabilizing gas cylinder, a safety valve and a water injection pipeline, and is arranged on a supporting platform above the side of the pressure vessel. The temperature control and heating system can automatically cut off the power according to the maximum temperature in the reactor; constant power heating, or gradually reduce the power according to the actual reactor core decay heat curve.

[0032] The outer surface of the integrated pressure vessel is covered with insulation material. At the same time, the measuring instruments in the primary circuit are flow meter (set in the descending section of the two loops to measure the natural circulation flow of the primary circuit), thermocouple (set at the end of the ascending section to monitor the fluid temperature and cut off the power in time; at the end of the descending section), pressure gauge (set at the regulator to maintain the system pressure stability), and liquid level gauge (set in the regulator for liquid level monitoring to facilitate timely water replenishment).

[0033] The operating environment of the integrated design loop for energy conversion and waste heat removal (secondary loop) is specifically designed with an operating pressure of 0.2MPa and a temperature range of 30-120°C. The fluid working medium is in a single-phase to two-phase fluctuation state, and a phase change occurs between the steam generator and the condenser. This is used to avoid relying on natural circulation drive, which is prone to flow instability.

[0034] In this embodiment, the integrated design loop for energy conversion and waste heat discharge (secondary loop) specifically includes a steam turbine simulation body, a condenser, a deaerator simulation body, a feed pump simulation body pipeline, a No. 1 water tank and a valve; wherein the steam turbine simulation body is a steam turbine in the natural circulation process, which does not output shaft work to the outside and does not generate electrical energy, and the blades and the like are considered to be stationary, and there is no heat exchange with the surrounding environment, and therefore, it is treated as a resistance component; in this embodiment, a resistance valve is used for simulation, and attention is paid to the inlet and outlet pressure difference, the flow rate determined by the size and other parameters, and bypass pipelines are respectively set on the two loops.

[0035] The condenser is close to a real condenser device. Since the establishment of natural circulation has high requirements on heat exchange capacity, the experimental modeling should be as accurate as possible. Therefore, in this embodiment, a condenser device close to the design of marine nuclear power is used. The overall design of marine nuclear power uses an annular condenser, and the upper part is directly connected to the end of the turbine volute, without a thin pipe in the middle. In this embodiment, a shell and tube heat exchanger is adopted, and the steam goes to the shell side and the cooling water goes to the tube side. The condenser itself has a certain elevation difference, which improves the natural circulation capacity of the cooling water on the tube side. The overall shape of the condenser is a high, thin, long flat plate, and a structural design with low flow resistance is selected.

[0036] In the deaerator simulation body, the deaerator does not have a heat exchange function. In the waste heat discharge stage, it can only bring a certain flow resistance. In general, the deaerator adopts a spray valve design, and the flow resistance will be greatly increased. Therefore, in the natural circulation heat discharge stage, it is necessary to bypass and isolate the deaerator to improve the natural circulation capacity of the entire system. In the simulation of this embodiment, a valve is also used to simulate the deaerator, and bypass pipes are respectively set on the two loops.

[0037] When there is no shaft power input and output, the thermal hydraulic characteristics of rotating machinery such as pump equipment in the feed pump simulation body pipeline are similar to those of a steam turbine, and there is no heat exchange. In the simulation of this embodiment, valves are also used for simulation. Since the experimental research also includes the study of natural circulation heat dissipation startup, transition, steady state, transient and other characteristics, it is necessary to set a feed pump loop, an orifice resistance simulation body loop, and a bypass loop in the loop.

[0038] In this embodiment, water tank No. 1 is used for loop filling and drainage, and its specific design volume is 1m 3 The No. 1 water tank on the left and right is at the same height as the water supply pump. The No. 1 water tank is connected to the natural circulation loop through a pipeline. Water is filled before operation and water is stored after operation. However, the natural circulation is isolated from the loop during actual operation.

[0039] All equipment in the secondary circuit is wrapped with insulation material, and the heat leakage rate is <1%. Water filling and drainage ports are set at the lowest end of the water tank and the circuit for cleaning the equipment and draining the fluid. Support structures are set for each key equipment, especially the condenser, flow meter (set at the inlet and outlet sections of the steam generator), thermocouple (set at the inlet and outlet sections of the steam generator, the inlet and outlet of the condenser, and the No. 1 water tank for real-time monitoring), pressure gauge (set at the top of the secondary circuit and the lowest end of the secondary circuit), and liquid level meter (set for water level monitoring in the No. 1 water tank; bypass water level monitoring on the outside of the steam generator to monitor the height of phase change in the steam generator in real time).

[0040] The operating environment of the condenser cooling water loop (three loops) is specifically designed to be under normal pressure conditions with a temperature range of 20-80°C. The fluid working medium is in a single-phase state, boiling occurs, and natural circulation occurs on the condenser tube side. The heat source comes from the heat release of the condenser steam, and the cold source comes from the cold water in the water tank. In the design of marine nuclear power sources, it comes from seawater. In the simulation of this embodiment, the low-temperature environment of marine flow is simulated by slowly injecting and discharging equal flow rates of cold water in the No. 2 water tank.

[0041] In this embodiment, the condenser cooling water circuit (three circuits) specifically includes the condenser tube side and water tank No. 2; the condenser tube side adopts a U-tube layout, and multiple independent groups of pipelines are arranged in the condenser, which are synchronously connected to the cooling water tank No. 2 to ensure natural circulation capacity, as well as flow distribution and heat discharge balance of each loop.

[0042] The volume of water tank No. 2 is 2m 3 , open design, cold water of equal flow rate is slowly injected and discharged from the top side and the bottom side, the water injection temperature is 23℃, the pipe on the condenser tube side is connected to the area below the water tank side (not on the same side as the cold water injection and discharge port), the water inlet and outlet have a certain height difference, and a water pump is installed between the water tank and the condenser cooling water inlet pipe; the measuring instruments specifically include flow meter (installed in the inlet section of the condenser tube side), thermocouple (installed in the inlet section, outlet section and cold water pipe inlet section of the condenser tube side), and liquid level meter (installed in water tank No. 2).

[0043] This embodiment verifies the system operating characteristics under the following operating conditions: (1) system startup, (2) transition from forced circulation to natural circulation, (3) stable operation of natural circulation, and (4) natural circulation system response under power transient conditions. The purpose is to form natural circulation in a multi-loop coupled system and couple to discharge the simulated body heat of the core.

[0044] The specific verification steps are:

[0045] (1) System equipment and commissioning, primary circuit sealing inspection, filling water into No. 1 and No. 2 water tanks, and testing whether the temperature meets the requirements.

[0046] (2) Inject water into the primary circuit from the top water injection pipe to fill the pressure vessel with water, and then perform the exhaust operation; open the gas cylinder, adjust the ventilation volume, maintain the pressure in the stabilizer at 1.0 MPa, and ensure that the water level in the stabilizer is above the warning line.

[0047] (3) Open the No. 1 water tank isolation valve and start the secondary circuit water supply pump. At the same time, turn on the electric heater to make the secondary circuit circulating water temperature reach 36°C; when the temperature meets the requirements, turn off the electric heater.

[0048] (4) Turn on the electric heater, adjust the power to above the set value, continue heating until the water temperature of the first circuit reaches 165°C, close the No. 1 water tank isolation valve, open the energy-converting circuit valve, and continue to remove the heat of the first circuit in a forced circulation manner; and assist the first circuit to establish natural circulation, and record the flow rate of the first circuit and the temperature values ​​of each temperature measuring point at this time.

[0049] (5) Reduce the power of the electric heater to the core residual heat level, turn off the second-loop feed water pump and the third-loop water pump, so that the second and third loops can establish a multi-loop coupled natural circulation based on their own density difference, and record the flow of each loop and the temperature value of each temperature measuring point in real time (multi-loop natural circulation start-up, transition, and stable operation characteristics).

[0050] (6) Increase the power of the electric heater to the set value and record the transient changes of parameters such as the flow rate of each loop in the multi-natural circulation loop and the temperature value of each temperature measuring point.

[0051] (7) Reduce the power of the electric heater to the set value and record the transient changes of parameters such as the flow rate of each loop in the multi-natural circulation loop and the temperature value of each temperature measuring point.

[0052] (8) Cut off the power supply of the electric heater, turn on the water supply pumps of the second and third circuits, and continue to run them until the temperature in the two circuits drops to room temperature. Turn off the water supply pumps, close the gas cylinder, drain the circuits, tidy up the equipment, and complete the experiment.

[0053] This embodiment conducts research on the operating characteristics and impact analysis of the multi-loop natural circulation coupled heat removal experimental system for different accident conditions, studies the flow instability of single-phase and two-phase coupled natural circulation with low head difference and high flow resistance, obtains the transient response characteristics of the system, and verifies the feasibility and robustness of the design and operation of the integrated circuit for energy conversion and waste heat removal of marine nuclear power sources.

[0054] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A multi-loop natural circulation coupled heat removal experimental system, characterized by: It includes an integrated pressure vessel, an integrated design circuit for energy conversion and waste heat removal, a condenser cooling water circuit, thermal insulation materials and measuring instruments; the thermal insulation materials are coated on the heat removal experimental system to reduce energy leakage; the measuring instruments are arranged on the heat removal experimental system to measure and monitor the flow, temperature, pressure and liquid level; The integrated pressure vessel includes a heat exchanger, a pressure stabilizer system and a temperature control and heating system; the heat exchanger is a plate heat exchanger, the pressure stabilizer system is arranged on a supporting platform above the side of the pressure vessel, and the temperature control and heating system is used to automatically cut off the power according to the highest temperature in the stack; The energy conversion and waste heat discharge integrated design loop includes a steam turbine simulation body, a condenser, a deaerator simulation body, a feed water pump simulation body pipeline, a No. 1 water tank and a valve; the steam turbine simulation body is treated as a resistance component, the condenser adopts a shell and tube heat exchanger, the steam flows on the shell side, and the cooling water flows on the tube side. The condenser itself has a certain elevation difference to improve the natural circulation capacity of the cooling water on the tube side. The deaerator is simulated by a valve, the feed water pump simulation body pipeline is simulated by a valve, and the No. 1 water tank is used for loop filling and drainage; The condenser cooling water circuit includes a condenser tube side and a No. 2 water tank; the condenser tube side adopts a U-tube layout, and multiple independent groups of pipelines are arranged in the condenser, which are synchronously connected to the cooling water tank No. 2 to ensure natural circulation capacity, as well as flow distribution and heat discharge balance of each loop; the No. 2 water tank is used to simulate the low temperature environment of ocean flow by slowly injecting and discharging equal flow rates of cold water.

2. According to claim 1, a multi-loop natural circulation coupled heat removal experimental system is characterized by: The integrated pressure vessel is specifically designed to have an operating pressure of 1 MPa, a fluid temperature range of 135-180°C, and is single-phase in the test heating section. The pressure vessel is made of 304 stainless steel, and has a heating element through hole and a core simulation body at the bottom for simulating core heat release by electric heating.

3. The multi-loop natural circulation coupled heat removal experimental system according to claim 2 is characterized by: A distance of at least 0.2 m is provided between the integrated pressure vessel and the supporting platform to facilitate the arrangement of drainage and heating element wires.

4. The multi-loop natural circulation coupled heat removal experimental system according to claim 3 is characterized by: A drain channel is provided below the integrated pressure vessel for draining water from the vessel.

5. The multi-loop natural circulation coupled heat removal experimental system according to claim 1 is characterized by: The operating environment of the integrated energy conversion and waste heat removal design loop is specifically designed to have a design operating pressure of 0.2 MPa, a temperature range of 30-120°C, a fluid working medium in a single-phase to two-phase fluctuation state, and a phase change occurs between the steam generator and the condenser to avoid flow instability.

6. The multi-loop natural circulation coupled heat removal experimental system according to claim 1 is characterized by: The operating environment of the condenser cooling water circuit is specifically designed to be under normal pressure conditions with a temperature range of 20-80°C. The fluid working medium is in a single-phase state and boils, and natural circulation occurs on the condenser tube side. The heat source comes from the heat release of the condenser steam, and the cold source comes from the cold water in the water tank.

7. The multi-loop natural circulation coupled heat removal experimental system according to claim 1 is characterized by: The measuring instruments are specifically flow meters, thermocouples, pressure gauges and liquid level gauges, which are used to measure and monitor the flow, temperature, pressure and liquid level of the heat removal experimental system.

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